This invention relates to shipping pallets equipped with one or more readable devices, such as, for example, radio frequency identification (RFID) tags, microprocessors, sensors, and the like. More specifically, it relates to those of such pallets that have a deck-boards-and-stringers or deck-boards-and-stringer-and-blocks type of construction wherein the deck boards do not cover the entire load-bearing surface of the pallet. Pallets utilizing this type of construction usually are made of wood or structural plastic and typically include but are not limited to: stringer pallets, two-way stringer pallets, modified four-way stringer pallets, heavy duty stringer pallets notched for four-way entry, stevedore type double wing pallets, stevedore type single wing pallets, single faced skids, grocery industry four-way pallets, limited use stringer pallets, block pallets, perimeter base block pallets, and standard reversible pallets, but do not include panel deck pallets or full deck pallets.
A problem in equipping a shipping pallet or skid of the deck board type construction with a readable device, such as an RFID tag, is where and how to attach or enclose the device so that it is not exposed to lifting-fork impact or subjected to the load borne by the pallet. U.S. Pat. No. 6,814,287 to Chang et al. suggests placing the RFID tag in a deep, cylindrical cavity in one of the stringers, enclosed in a sealed housing that is friction-held in the cavity. One drawback of that arrangement is that the removal of so much material from the stringer weakens it. Another drawback is that the tag is practically surrounded by a wall of wood or man-made material that is so thick that it can be a serious barrier to RF transmission between the tag and an RFID-interrogation device used to “read” information stored on the tag. Wood used in shipping pallets typically has a moisture content of ±11%. The moisture content presents a significant barrier to RF transmission between the tag and the RFID-interrogation device. If the moisture content is reduced through heating, the wood becomes brittle and subject to splintering, possibly rendering the shipping pallet useless.
U.S. Pat. No. 6,669,089 to Cybulski et al. suggests placing the RFID tag in or on one of the deck boards or, alternatively, on a chamfered inside corner of one of four corner blocks used to support flat-lying stringer boards that underlay the top deck boards. As for the attachment of the tag to the surface of a deck board or corner block, because of the extremely rugged treatment a shipping pallet can receive, that still exposes the tag to forces that can damage or dislodge it, even if it is located between two deck boards or on the inside edge of a corner block. Debris from above can be forced down between the deck boards by the weight of a load on the pallet, possibly causing harmful impact or pressure on any tag attached to the vertical inside edge of a deck board. If mounted on the inside chamfered edge of a corner block, the tag may not be as exposed to down-forced debris, but it is still somewhat vulnerable to dislodgement or breakage by misdirected forklift tines. Additionally, the wooden block presents a serious barrier to RF transmission between the tag and any RFID-interrogation device used to “read” information stored on the tag.
As for placing the RFID tag inside one of the deck boards, the cavity required weakens the board. Moreover, if the board is plastic it can be difficult and costly to choose a type of RFID tag that will withstand the thermoforming temperatures required to mold the board with the tag inside. A cavity could be milled out of the plastic board later, but that operation adds to the cost of manufacture as well.